Production of full-flavored stable essential oils



'% p-CYIVIENE 09 Dec. 27, 1966 PERCENT PRODUCTION OF FULL-FLAVORED STABLE ESSENTIAL OILS Filed 001;. 12, 1961 IO I Iscppeoronce 6 of gommu-Ierpmene 2 I v 4 FIG.'I

Formation of 2 p-cymene I I l I I IO 3o 40 DAYS LLI Z LIJ 4Q 2 O Y FIG. 2 c1 20 PRODUCT? IO 1 5 2 0 25 DAYS FIG?) I I ATTORNEYS United States Patent i 3,294,550 PRODUCTION OF FULL-FLAVORED STABLE ESSENTIAL OILS Robert M. Ikeda, Pasadena, and William L. Stanley, Richmond, Califi, Sadie H. Vannier, Bethesda, Md., and Lawrence A. Rolle, Altadena, Califi, assignors to the United States of America as represented by the Secretary of Agriculture Filed Oct. 12, 1961, Ser. No. 144,802 7 Claims. (Cl. 99-140) A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates in general to the treatment of essential oils. A particular object of the invention is the provision of methods for producing essential oils in a state combining stability with retention of natural aroma. Further objects and advantages of the invention will be obvious from the following description wherein parts and percentages are by weight unless otherwise specified. The expression terpene used herein is inclusive of sesquiterpenes.

In the drawing: FIGURE 1 is a graph which illustrates the disappearance of gamma-terpinene and the formation of p-cymene during deterioration of a sample of lemon oil originally containing 11.5% of gamma-terpinene. FIG. 2 is a graph illustrating the formation of p-cymeue from gamma-terpinene. FIG. 3 is a graph illustrating the stability of the product of the invention.

Essential oils are widely used in perfumes, pharmaceuticals, toilet-preparations, and as flavors in food products and beverages. It is well known that essential oils contain two principal types of components-(a) oxygenated compounds such as aldehydes, ketones, esters, alcohols, and the like, and (b) hydrocarbons of the terpene series. It is recognized that the terpene fraction oxidizes readily in air with the result that the essential oils develop unpleasant odors and flavors. In order to alleviate this difficulty, producers have placed on the market the so-called terpeneless oils. These, for the most part, retain solely the oxygenated compounds and are thus more stable on storage.

The production of terpeneless essential oils may be achieved in various ways, for example, by distillation, selective extraction, extraction combined with distillation, or by the adsorption and elution method of Kirchner et al., U.S. Patent 2,712,008.

The known methods of producing terpeneless essential oils are subject to two primary disadvantages. The first is that removal of the terpenes from the oil causes a marked change in the aroma of the oil; the remaining oxygenated components do not exhibit the full bouquet of the natural oil. In effect, the terpeneless oils have an unnatural aroma because they are lacking in the terpene components. A second factor is that removal of the terpenes involves a very substantial loss of material because in many cases the terpenes make up the bulk of the natural oil. For example, Kirchner et al. show that treatment of 100 grams of lemon oil resulted in only 6 grams of terpeneless oil. Since essential oils are initially quite expensive, it is obvious that such low yields render the terepeneless products useful only in very specialized areas.

In accordance with the invention, the disadvantages outlined above are obviated in a simple yet effective manner. In essence, our invention involves providing essential oils which retain the oxygenated compounds and most of the original terpene constituents but which are essentially free from gamma-terpinene. The advantages of the invention include the following: In the first place, since the bulk of the original terpenes is retained, the product of the invention retains essentially all the natural aroma of the natural essential oil. In the second place, since the especially la-bi-le compound gamma-terpinene has been removed, the product is stable and can be stored for long periods Without development of the unpleasant odor generally termed cymey in the industry.

The importance of removing gamma-terpinene from the essential oil will be evident from the following explanation: Previously, it was known in a general sense that terpenes are oxidizable and lead to development of un natural aromas in essential oils. However, it was not previously known that gamma-terpinene plays the critical role in the instability of essential oils. Thus it has long been known that the deterioration of certain essential oilsparticularly lemon oilis characterized by the development of a cymey odor, due to the formation of p-cymene. Previous investigators [Strausz, Perfumery Essential Oil Record, vol. 38, page 262 (1947) and Guenther, The Essential Oils, vol. II, p. 332 (1949)] believed that p-cymene was formed from citral, naturally present in lemon oil, by the following mechanism:

Acid catalyzed hydration, C OH dehydration and cyclization 0% C t & 5

H2 H0 H $11 0 s R R R R Citral p-Cymene (R is the 0 H radical) Our researches, however, showed that the precursor of p-cymene is not citral but gamma-terpinene. The fact that citral is not implicated in the formation of p-cymene was indicated by the following experiment: (a) A sample of citral which had been held at room temperature for over 5 years without special precautions for excluding air was analyzed for p-cymene by a chromatographic method. No p-cymene could be detected. cmfwy c-mfw crnfw emf crnf orange oil was prepared by adding the required amount of a fresh sample of citral to orange oil containing about 0.03% citral and only a trace of gamma-terpinene. The orange oil-citral mixture was divided into two SO-ml. portions. One portion was transferred to an empty 250-ml. flask and the other to a 500-ml. flask containing 200 ml. of 6% aqueous citric acid solution. The flasks were stoppered to minimize evaporation losses of the lower boiling components and held at room temperature and under the usual lighting of the laboratory. Samples were iemoved periodically for analysis. During the storage period the stoppers were removed from time to time to replenish the air above the samples. Analysis of the samples after a period of 7 months showed no detectable quantity of p-cymene. On the other hand, the direct implication of gamma terpinene in producing p-cymene was shown by the following experiments: (c) One hundred and fifty m1. of lemon oil (having a natural content of 11.5% of gammaterpinene) was placed in a 250-ml. flask, loosely stoppered with glass wool and allowed to stand at room temperature. The content of p-cymene and gamma-terpinene was followed over a period of 3 months. The results are plotted in FIG. 1. In this figure curve 1 represents the disappearance of gamma-terpinene and curve 2 represents the formation of p-cymene. In another experiment ((1), a 7-ml. sample of gamma-terpinene was placed in a 50-ml. flask stoppered with a cotton plug and held at room temperature. From time to time, the material was analyzed for p-cymene by an infrared spectrophotometric method. The results are plotted in' FIG. 2. It was concluded from the above experiments that the formation of p-cymene is caused by oxidation of gamma-terpinene, particularly because the disappearance of gamma-terpinene can be accounted for by the appearance of p-cymene.

The preparation of the products of the invention may be efiectuated by various techniques generally known to chemists involving such conventional unit operations as distillation, extraction, and adsorption on adsorbent materials followed by elution with selective solvents, etc. As

an example, the essential oil may be subjected to distillation (preferably under vacuum to avoid heat damage to the oil) using conventional equipment to segregate fractions of difierent boiling ranges from the oil. The fraction containing the gamma-terpinene is discarded Whereas the fractions containing the oxygenated components of the essential oil plus the fractions containing the bulk of the terpenes other than gamma-terpinene are combined to form the essential oil product of the invention. Another plan is to extract the oxygenated components from the essential oil with a suitable solvent such as dilute alcohol. The residual terpenes are then distilled to remove the gamma-terpinene. The remaining terpenes are then mixed with the oxygenated components obtained in the extraction procedure. In another system the essential oil is treated with chemical agents to isolate the oxygenated components. The residual terpenes are subjected to distillation to remove the gamma-terpinene and the remaining terpenes are mixed with the oxygenated components which were isolated by the chemical treatment. As an example of a chemical treatment for segregating the oxygenated components from the terpenes one may employ the technique disclosed by us in our co-pending application, Serial No. 109,464, filed May 11, 1961, issued Oct. 12, 1965, as Patent No. 3,211,740. This technique involves reacting the essential oil with a hydrazine derivative such as Girard reagent '1; (wan s-euro ONH-NH) to convert the aldehyde and ketone components of the essential oil into water-soluble hydrazone derivatives, diluting the reaction system with water, extracting the terpene constituents with an organic solvent, then reacting the hydrazone derivative with formaldehyde to regenerate the original aldehyde and ketone components. The terpene constituents removed in the extraction step are fractionated to remove gamma-terpinene and the remaining terpenes are admixed with the separated aldehyde and ketone components. Another chemical method for removing gammaterpinene involves the use of clathrating agents such as urea or thiourea.

In a preferred modification of the invention, the essential oil is treated by the adsorption-elution process of Kirchner et al., US. Patent 2,712,008, in order to isolate the terpenes from the oxygenated compounds. Following this step the separated terpene fraction is subjected to distillation to segregate gamma-terpinene from the remainder of the terpenes and the latter is admixed with the oxygenated components. Although the details of the Kirchner et al. process are set forth in the patent specification, it may be appropriate to recapitulate here the essentials of the process. The essential oil to be treated is adsorbed on a finelydivided adsorbent such as silica, alumina, magnesium oxide, or silicic acid, the latter being preferred. The adsorbent containing adsorbed essential oil is then eluted with a terpenophilic solvent-such as hexane, carbon tetrachloride, petroleum ether or other volati-le petroleum distillatein order to selectively remove the terpene components from the adsorbent. The adsorbent is then eluted with an oxygenated organic solventsuch as ethyl acetate, diethyl ether, dioxane, acetone, ethanol, etc.-in order to elute the oxygenated components of the essential oil. This eluate is subjected to conventional treatment such as distillation to remove the eluting solvent. The first eluate is distilled to remove solvent and gamma-terpinene and the remaining terpenes are mixed with the oxygenated components. In many cases, the terpenes which We admix with the oxygenated compounds are those which have boiling points below that of gamma-terpinene since these low-boiling terpenes constitute the najor part of the total terpene fraction and contain most. of the components of desired aroma. (The boiling point of gamma-terpinene is 183 C. at atmospheric pressure.) Typically, in lemon oil these lower-boiling components will include a-pinene, fi-pinene, thujene, sabinene, myrcene, and limonene.

The use of the adsorption-elution technique described above is preferred because application of heat to the essential oil components is reduced to a minimum, hence deterioration of the components is minimized.

Although the invention is of particular applicability to the treatment of lemon and lime oils it may be applied to any essential oil which naturally contains gamma-terpinene. Thus, in addition to lemon oil and lime oil, the invention may be applied to oils of coriander, marjoram, thyme, cedar leaf, bergamot, cascarillo, origanum, nutmeg, and the like.

The products of the invention may be used for any of the purposes for which essential oils are employed as in perfumes, pharmaceuticals, toilet preparations, food products, beverages, etc. The products are particularly adapted for use in food products, for example, in restoring the flavor to concentrated or dehydrated fruit juices, because they contain only the natural components of the essential oil and because of their good aroma combined with stability on storage.

The invention is further demonstrated by the following illustrative example.

A sample of lemon oil was procured. This oil contained 2.82% total aldehydes and 2.23% citral. The terpenes present in the oil were as follows:

One pound (454 grams) of the lemon oil was adsorbed on an 800-ml. column of finely-divided silicic acid. The silicic acid was eluted with 2,500 ml. of hexane to elute the terpene constituents (Eluate A). The silicic acid column now free from terpene constituents was eluted with 1,000 ml. of ethanol to elute the oxygenated components (Eluate B).

The hexane was stripped from Eluate A and the remaining terpenes were distilled under vacuum in a spinningbrush rectifying column. The terpenes boiling up to 69.5 C. at 20 mm. pressure were condensed and collected (Fraction C, 247 grams). The residue, weighing 134 grams and containing 67% limonene, 31% gammaterpinene, and 2% para-cymene (the last apparently formed during the distillation) was discarded.

The ethanol and water was stripped from Eluate B and to the resulting oxygenated components was added Fraction C to provide 280 grams of essential oil free from gamma-terpinene. This product contained 3.46% total aldehydes and 2.68% citral. The terpenes present in the product were as follows: a-pinene 2.5%, fl-pinene 20.9%, mycrene 1.8%, limonene 74.8%, gamma-terpinene-trace (less than 0.2%.)

Organoleptic tests on the product indicated that it had an aroma more nearly like that of natural lemon oil than did a material prepared by removing all the terpenes from the original lemon oil stock.

A sample of the product and a sample of the original lemon oil were stored in open vessels at room temperature, exposed to ordinary room lighting conditions. From time to time during the storage, samples of the two materials were subjected to an analysis for p-cymene. The results are plotted in FIG. 3. In this figure, the formation of p-cymene in the product is represented by curve 1' and the formation of p-cymene in the untreated lemon oil is represented by curve 2'. The stability of the product is clearly evident from the figure. For example, after 27 days storage, the product of the invention still contained less than 1% p-cymene whereas the untreated lemon oil contained more than of p-cymene.

Having thus described the invention, what is claimed is:

1. The process which comprises separating an essential oil selected from the group consisting of lemon and lime oils into a fraction containing the terpene constituents of the essential oil and a fraction containing the oxygenated constituents of the essential oil, removing from the terpene firaction essentially all the gamma-terpinene contained therein and combining the bulk of the remaining terpene fraction with the fraction containing the oxygenated compounds.

2. The process of claim 1 wherein the essential oil is lemon oil.

3. The process of claim 1 wherein the essential oil is lime oil.

4. The process which comprises separating lemon oil into a first fraction containing the terpene constitutents of the lemon oil and a second fraction containing the oxygenated (non-terpene) constituents of the lemon oil, subjecting the first fraction to distillation and collecting the terpenes having boiling points below that of gamma-terpinene and blending these terpenes with the said second fraction.

5. An essential oil product consisting essentially of the oxygenated components of the natural essential oil and the bulk of the terpene components of the natural essential oil but essentially free from gamma-terpinene, said natural essential oil being a member of the group consisting of lemon and lime oils.

6. A lemon oil product consisting essentially of the oxygenated components of natural lemon oil and the bulk of the terpene components of natural lemon oil but essentially free from gamma-terpinene.

7. A lime oil product consisting essentially of the oxygenated components of natural lime oil and the bulk of the terpene component of natural lime oil but essentially free from gamma-terpinene.

References Cited by the Examiner UNITED STATES PATENTS 6/1955 Kirchner et a1 260-2366 OTHER REFERENCES A. LOUIS MONACELL, Primary Examiner.

IRVING MARCUS, WALTER A. MODANCE, I. A.

PATTEN, I. M. GOLIAN, R. N. JONES,

Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,294,550 December 27, 1966 Robert M. Ikeda et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, l ine 40, strike out "cmfwy cmfw cmfw cmf cmf" and insert instead (b) A 4% mixture of citral in Signed and s ealqd this 12th day of September 1967.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attcsting Officer Commissioner of Patents 

1. THE PROCESS WHICH COMPRISES SEPARATING AN ESSENTIAL OIL SELECTED FROM THE GROUP CONSISTING OF LEMON AND LIME OILS INTO FRACTION CONTAINING THE TERPENE CONSTITUENTS OF THE ESSENTIAL OIL AND A FRACTION CONTAINING THE OXYGENATED CONSTITUENTS OF THE ESSENTIAL OIL, REMOVING FROM THE TERPENE FRACTION ESSENTIALLY ALL THE GAMMA-TERPINENE CONTAINED THEREIN AND COMBINING THE BULK OF THE REMAINING TERPENE FRACTION WITH THE FRACTION CONTAINING THE OXYGENATED COMPOUNDS.
 5. AN ESSENTIAL OIL PRODUCT CONSISTING ESSENTIALLY OF THE OXYGENATED COMPONENTS OF THE NATURAL ESSENTIAL OIL AND THE BULK OF THE TERPENE COMPONENTS OF THE NATURAL ESSENTIAL OIL BUT ESSENTIALLY FREE FROM GAMMA-TERPINENE, SAID NATURAL ESSENTIAL OIL BEING A MEMBER OF THE GROUP CONSISTING OF LEMON AND LIME OILS. 